1. The Field of the Invention
The present invention relates to polymer-micelle complexes.
2. Description of Related Art
Cleaning product formulations, including those which contain common antimicrobial agents such as quaternary ammonium compounds and biguanides such as chlorhexidine and alexidine, rely on surfactants and mixtures of surfactants to deliver cleaning (detergency) and antimicrobial efficacy. A key aspect of these processes is the interaction of the surfactants and antimicrobial agents with the solid surfaces of the materials being cleaned, as well as the surfaces of microorganisms, together with the effects of the formulations on the air-water interface (surface tension). Reduction of the surface tension of aqueous formulations, which is directly related to the effectiveness of the wetting of solid surfaces and hence the detergency and antimicrobial processes, can be manipulated through the use of mixtures of surfactants, as is known in the art.
At a molecular level, surfactants and surfactant mixtures in aqueous media exhibit the ability to adsorb at the air-water, solid-water, and oil-water interfaces, and this adsorption is hence responsible for a wide range of phenomena, including the solubilization of oils in the detergency process, the changes in the properties of solids and dispersions of solids, and the lowering of the surface tension of water. Adsorption of surfactants at interfaces is generally known to increase with surfactant concentration up to a total surfactant concentration known as the critical micelle concentration (CMC). At the CMC, surfactants begin to form aggregates in the bulk solution known as micelles, in equilibrium with the monomeric species of surfactants which adsorb onto the interfaces.
The details of the structures and sizes of the micelles, as well as the properties of the adsorbed layers of surfactants or surfactant mixtures, depend on the details of the molecular shape and charges, if any, on the hydrophilic “headgroups” of the surfactants. Strongly charged headgroups of surfactants tend to repel each other at interfaces, opposing the efficient packing of the surfactants at the interface, and also favoring micelle structures that are relatively small and spherical. The charged headgroups of many surfactants, such as the quaternary ammonium compounds, will also introduce a counterion of opposite charge, for example a chloride or bromide ion, into formulations.
It is known that the nature of the counterion can affect the repulsion between charged surfactants in micelles and adsorbed layers through a partial screening of the headgroup charges from one another in surfactant aggregates like micelles. It is also well known that addition of simple electrolytes, such as sodium chloride, into aqueous solutions can also be used to increase the screening of like headgroup charges from each other, and thus is a common parameter used to adjust the properties of surfactant micelles, such as size and shape, and to adjust the adsorption of surfactants onto surfaces.
Addition of significant amounts of simple electrolytes into many formulations, such as hard surface spray cleaners or nonwoven wipes loaded with a cleaning lotion, is undesirable due to residues left behind upon drying of the formulations. An alternative method to adjusting the properties of such formulations, including the wetting of solid surfaces and the antimicrobial activity, is to include significant amounts of volatile organic solvents such as lower alcohols or glycol ethers. Volatile organic solvents, however, are coming under increasing regulation due to their potential health effects, and are not preferred by the significant fraction of consumers who desire efficacious cleaning and disinfecting products with a minimum of chemical actives, including volatiles. In the healthcare industry, efficacious formulations comprising quaternary ammonium compounds and lower alcohols are known, but are viewed as having shortcomings in terms of the potential for irritation of confined patients. Such products pose similar risks to cleaning and clinical personnel who may be exposed to such products on a daily basis.
There is an increasing interest from consumers, and a known need in the healthcare and housekeeping industries, to reduce the number of microorganisms on fabrics while using familiar equipment such as washing machines. Concentrated products are required for such an application, due to the high dilution level of the product in the rinsewater, typically by a factor of about 600 times dilution. In the case of formulations comprising quaternary ammonium compounds, high concentrations of the quaternary ammonium compounds in the concentrate are needed in order to ensure an adequate amount of adsorption occurs in a kinetically relevant time onto the microbes under dilution use conditions. As detailed above, it is desirable, yet very difficult, to manipulate (i.e., reduce) the CMC of the quaternary ammonium compound in such an application. Thus very high concentrations of quaternary ammonium compounds, which tend to be hazardous to the skin and eyes, are used in the concentrates, in combination with high temperatures and long exposure times.
Thus, there is an ongoing need for methods and compositions offering fine control of the properties of surfactant aggregates comprising cationic species, especially antimicrobial species such as quaternary ammonium compounds and biguanides.